The use of sandblasting to clean steel structures before applying paint is associated with severe and rapidly progressive silicosis. High morbidity and mortality rates have been noted within a few years of exposure. The U.S. Department of Labor has estimated the number of workers engaged in sandblasting to be 78,000. Recognition of these hazards led to the prohibition of sandblasting in Europe and Australia; in the U.S., sand substitutes are now increasingly being used. They are derived from coal ash residues and slag from smelting furnaces, and comprise various proportions of amorphous silicates of Fe, Al, Ca, Mg and Ti. The free silica content is only 0.03%. The objective of this project is to develop a rat model to assess the pulmonary fibrogenic potential of sand substitutes. Fibrotic effect from prolonged exposure to the substitutes will be investigated in both normal and silicotic rats. Silicosis will be induced in one group, followed by exposure to the substitute; the second group will be exposed only to the substitute. After exposure, both groups will be followed for an additional twelve months. Appropriate control rats will be maintained for comparisons. Rats will be sequentially sacrificed for histologic, biochemical assay of collagen, and tissue mineral content evaluations. This study will assess for the first time the safety of these substitutes. We believe this rat model will have application in delineating and predicting the potential occupational hazards for abrasive blasters with and without pre-existing silicosis. Occupational exposure standards are based on the assumption that the risk of any particular agent is not influenced by exposure to other environmental factors. This study will provide important information on the risk of lung fibrosis from biologic interactions between different inhaled agents, which could affect the future development of occupational standards. More specifically, this project will demonstrate increased risk of progression of silicosis if silicotic sandblasters use these substitutes.